MAVIS: adaptive optics module final design

Abstract

The Adaptive Optics Module (AOM) of MAVIS will be the only MCAO facility at the VLT, and will allow it to exploit the capabilities of the Adaptive Optics Facility of UT4, also in the wide field regime. The post-focal instrumentation consists of an imager and an IFU spectrograph, both covering the visible band; a third port is also available. The AOM will provide 30" FoV AO correction, controlling a total of more than 4500 modes, spread across its suite of three deformable mirrors (one being the telescope Deformable Secondary Mirror). The AOM includes four main subsystems, being a common path post focal relay, providing DMs correction, field derotation and atmospheric dispersion compensation; the Shack-Hartmann-based natural and laser guide star wavefront sensors; and the real time computer. The main challenge of this MCAO system is that it shall provide good AO correction in a wide field and in a short band domain. This led to an overall control scheme that includes, together with the main MCAO control loop, some auxiliary loops and setup and tracking devices to be controlled while in operation, which increases the system complexity. The project went through its FDR in October 2025, when the AOM scheme and opto-mechanical design were confirmed and approved. In this paper, we present the Final Design of the AOM, together with the main results of our analysis, devoted to confirming the compliance with performance and stability requirements.